Fire Separation Allowable areas.

[Question That]

New Construction type IIB. I have a 12,000 sf building separated into two fire areas by a 2 hour fire barrier wall.
It's my understanding that because of the separation I'm allowed/ required to use section 903 to determine what area sf is allowed for the two separated areas which are A2 & M. For A2 you are allowed <5000 sf and <100 occupants until you hit the requirement for sprinkler system. For M you are allowed <12,000 sf with no number of occupants specified until you reach the sprinkler threshold.
So the way I'm interpreting this is that for the A2 occupancy I can have up to 5000 sf and for the M occupancy I can have up to 12,000 sf if I don't want to install sprinklers as long as I have the fire barrier wall.... which is what I have
What I'm not following is whether or not 508.4.2 still applies for this situation. If so (if my math is right), I don't meet the <= requirement and I have no idea why.
Can anyone help me get to the bottom of this?

 

[Jay Smith]

Read the last sentence of 503.1. If your wall between fire area is a fire wall that complies with 706, allowable area is calculated separately on each side of the wall.

 

[Jay Smith]

I should probably clarify that checking the fire resistance requirements in 706 confirms a 2-hour fire barrier does not meet the fire wall requirements for Group M, so the calculation for this as one building does apply. Make sure you include the frontage increase in the allowable area if your building is eligible for it.

 

[Question That]

Thanks Jay for the response! Some GREAT information in your comments and it's really appreciated!

Totally missed the 503.1 component! And IF I had the 3 hour wall I think I understand where you are headed with this.
But, since I only have a 2 hour fire barrier wall then that would mean that the whole 503.1 component doesn't apply.... at least that's my understanding of what you are meaning here.

So has me wondering what will happen if I change the wall to 3 hour and redo the calcs based on that. I will eventually.

AND, now that I've stumbled on the area increase whether or not I even need the fire barrier wall..... but my guess is I do.

Bottom line there are all these tables for different fire wall requirements for the different adjacencies and it's definitely confusing (to me) at best. Need to dig into it some more to get a good handle.

Anyway, for the time being if I keep the 2 hour wall that I already have AND include the frontage area increaseses it looks like I'm good.
I had just done the frontage increase calcs when I saw your post but not absolutely certain I applied them correctly based on using 508.4.2 "allowable building area" because it says nothing about area increases. BUT I think I'm covered because of 506.2.2 & 508.4.2 for mixed separated occupancies! At least thats what I'm hoping. IF that is the case then thinking that all I have to do to apply the area increases is multiply the "allowed areas" times the factor and add that to the allowed areas for the new allowed areas then run the formula to get to < or = to 1. Right?

Was not aware of the 3 hour requirement in table 706. I think what you mean is that per table 706.4 for IIB Assembly and Business I would only need 2 hour because of footnote "a"..... IIB construction. BUT, because I'm also Mercantile, the footnote went away so going to require 3 hour regardless. So, because of the most restrictive requirement need 3 hour..... right? That's what you mean correct?

So not able to get my head wrapped around the following:
Tables & Separtion Wall Requirements in code order-

• Table 508.4- Required separation of occupancies in hours
  • For A, B & M non sprinklered 2 hours
• Fire Wall Section, Table 706.4- Fire Wall Fire-Resistance Ratings
  • For A & B 3 hours (unless IIB) but 3hr for M so according to this table I'm stuck with 3 hours this project.
• Fire Barrier Section, Table 707.3.10-"Fire-Resistance-Rating Requirements for Fire Barriers, Fire Walls.... Between Fire Areas
  • For A, B & M 2 hours.

Just a little confused here....

But definitely thanks for your help!

 

[Question That]

Summary-
So, wondering now if I can get away with no fire wall/ Fire Barrier
If "need" Fire Barrier/ Fire wall then which one.
If "need" Fire Barrier/ Fire wall, does it need to be 2 or 3 hour.
And What ultimately makes the most sense if I have a .75 frontage increase factor available to me.....

 

[Jay Smith]

With a 2-hour fire barrier - For Group A-2 in construction type IIB you could have an allowable area of as much as 9,500 + (9,500 x 0.75) = 16,625 square feet if the frontage is the maximum all around the building. For Group M it could be as much as 12,500 + (12,500 x 0.75) = 21,875 square feet. The sum of the ratios will be less than 1.

With no fire barrier, the entire building must comply with the requirements of the more restrictive occupancy per 508.3.1 and 508.3.2. You would have a fire area of 12,000 square feet for purposes of 903.2.1.2 (Group A-2 sprinkler requirements).

 

[Question That]

Thanks again Jay. I had a couple of misconceptions and your explanation above cleared it up for me. Have my math right now and a much clearer understanding of the process.

 

[Paul Sweet]

You will hit the 100 occupant threshold for sprinklers in A-2 long before the 5000 SF threshold, since restaurants are one occupant per 15 SF.

 

[classicT]

You will hit the 100 occupant threshold for sprinklers in A-2 long before the 5000 SF threshold, since restaurants are one occupant per 15 SF.

Not necessarily given that the kitchen area associated with an A-2 is classified the same and is 200 gross.